There has been conventionally known an acoustic wave device in which an excitation electrode exciting an acoustic wave is located on a piezoelectric substrate and a functional element including the excitation electrode is sealed by a resin as disclosed in Japanese Patent Application Publication No. 2009-188844. In the aforementioned acoustic wave device, the resin seals the functional element so that an air-space (space) is formed above the excitation electrode.
In the conventional acoustic wave device, a resin is used as a sealing material, and thus the hermeticity is not sufficient, and the penetration of moisture damages the excitation electrode and decreases the reliability of the device.